Referring to FIG. 1A of the drawings, the reference numeral 100 generally designates conventional PCB that is adapted to use for four IR sensors, where the section 101 (for one of the sensors) is shown in greater detail in FIG. 1B. As shown, there is an integrated circuit (IC) seat 102 that is adapted to receive an IC that includes an IR sensor. For this configuration, the package for the sensor is a wafer level chip scale package (WCSP) that can be secured to the PCB 100 at IC seat 102 (for example) with eight solder balls. For each of the contact pads (which are located within the IC seat 102 and are adapted to be secured to a solder ball), there are traces 108-1 through 108-8 to provide electrical connections for the IC. Additionally, a capacitor seat 104 and resistor seat 106 are also shown. With this circuit layout, the traces (and all other conductive material) are laid out in a generally linear and symmetrical pattern.
Turning now to FIG. 2, the response of the four IR sensors, which are secured to the PCB 100, can be seen. When a black body is swept from 0° C. to 120° C. (as shown in FIG. 2), the average output voltage for the sensors varies by 10-to-1. For example, at 115° C., the sensor outputs vary between 55 μV and 550 μV. Clearly, repeatability is very poor. This drastic variation, however, can be attributed to the sensitivity of IR sensors. In particular, the IR sensors are very sensitive to thermal gradients between the sensor and the underlying PCB (i.e., PCB 100). Because the IR sensor is sensitive to changes in temperature between the “cold junction” and “hot junction,” when there are temperature variations or thermal gradients between the package and the underlying PCB (i.e., PCB 100), thermal gradients will induce small temperature changes of the hot junction which may cause the IR senor to generate false signals. Thus, thermal transients (which can create large thermal variations across a PCB) can create temperature readings (when detecting IR) that vary wildly.
One known solution for this problem is to employ a large thermal mass on the sensor package to reduce the effects of thermal gradients. This type solution is described by: Liess et al., “Reducing thermal transient induced errors in thermopile sensors in ear thermometer applications,” Sensors and Actuators A, Vol. 154, No. 1, 2009, pgs 1-6. However, using a large thermal mass increases the size and cost of the sensor, which can be prohibitive in some applications.
Therefore, there is a need for an improved apparatus and/or system that reduces thermal gradients.
Some other conventional systems are: U.S. Pat. No. 5,344,518; U.S. Pat. No. 6,637,931; U.S. Pat. No. 7,275,867; U.S. Pat. No. 7,435,964; and U.S. Patent Pre-Grant Publ. No. 2003/0016729.